Next week, MPs are expected to vote on whether to send it to the select committee phase and Mr McClay believes he has the numbers.
Mr Harawira said he wasn't a fan of gangs.
"But I really don't like it when government uses the media to create an image of gangs that causes people to be afraid, and then plays on that fear to ram through bills like this that deny gang members the civil rights that all New Zealand citizens enjoy.
"Apart from being a deeply racist piece of legislation, the majority of those targeted will be Maori. This bill has also been woefully underprepared."
In a statement, Mr Harawira asked who would enforce the bill and if classes would be run to ensure civil servants could correctly identify a gang patch.
"Does Mr McClay expect a doctor to refuse to treat an accident victim because he's wearing a patch?
"What will Mr McClay do to the civil servants who choose to ignore this law so that they can continue to build good relationships with gang members in their community?"
Mr Harawira said the bill deliberately targeted those on the fringe of society. "It will impact on Maori more than anyone else."
Mr McClay was disappointed with Mr Harawira's comments but agreed with him that gangs seemed to target young Maori men for membership.
However, the proposed law did not deal with race, it targeted gangs, irrespective of the makeup of their membership, he said.
"Sadly, Mr Harawira is trying to detract from the real issue here which is about the harm that gangs do to individuals, to communities and to our society. This bill will reduce the opportunity for gang intimidation in our schools and hospitals. It says `leave your patch at home if you are visiting a government building' and is similar to the policy adopted in a number of marae around the country over the last few years."
The bill, if passed into law, would be enforced by the police.
"As with any other law in New Zealand, should a person contravene it, they would be dealt with by a police officer."
Mr McClay said there was no expectation that teachers, nurses or any other public servant would be required to enforce this law.
"Just as they are not asked to catch a burglar or round up drug dealers."
The bill, as drafted, identified criminal organisations by naming gangs covered by its scope. It also defines gang insignia and purposely excludes tattoos, Mr McClay said.
The wearing of gang insignia in a government building would be prohibited except where there was justifiable cause.
Gangs covered by the bill:
Aotearoa Natives
Black Power
Devil's Henchmen
Filthy Few
Head Hunters
Hells Angels
Highway 61
Killerbeez
Magogs
Mongrel Mob
Mangu Kaha
Mothers
Nomads
Rebels
Road Knights
Satan's Slaves
Tribesmen